The lack of sufficient sensitivity and specificity of PSA as a screening modality for the diagnosis of prostate cancer underscores the importance of improving its operating characteristics to considerably improve the quality of predicting individual prostate cancer risk. Recently, serum-derived autologous antibodies (Ab) to individual prostate cancer-associated antigens (PCAA) received renewed attention as potential biomarkers for prostate cancer. The overall hypothesis of the proposal is that a multiplex approach that measures circulating autoantibodies against individual PCAA complement serum PSA tests to improve the prediction value of individual prostate cancer risk. Featuring an open-architecture design, the flow-cytometry based Luminex xMAP technology can be configured to detect autologous Ab to as many as 100 independent PCAA. However, to individually purify recombinant PCAA proteins and then conjugate with xMAP microspheres is difficult in practical terms. My lab has been focusing on identification of peptide epitopes from clinically relevant PCAA for the detection of autologous Ab present in serum samples. The simplicity of manipulating peptides over full-length proteins provides a unique opportunity to conjugate with microspheres applicable for the Luminex xMAP technology. To establish the Luminex-based multiplex assay for prostate cancer, we propose the following specific aims: 1) To configurate xMAP microsphere sets conjugated with B cell epitopes from a panel of clinically relevant PCAA previously defined in my lab;2) To assess the sensitivity and specificity for retrospectively differentiating prostate cancer as well as to prospectively monitor tumor progression by the multiplex assay. Serum sample from 75 subjects in each cohort of healthy donors, BPH patients, patients with prostatitis as well as prostate cancer patients will be available for the proposed study. This study will provide a novel multiplex assay to serve as a potential biomarker for prostate cancer in areas such as monitoring disease recurrence.